Investigating combustion efficiency and NOx emission reduction in fluidized bed ammonia-coal co-firing

Abstract

Ammonia, a carbon-free fuel, can significantly reduce CO₂ emissions when co-fired with coal in power plants. Fluidized bed combustion, known for its excellent gas-solid mixing and low NO_x emissions, is a promising method for ammonia-coal co-firing. However, challenges remain in optimizing ammonia injection and controlling nitrogen oxide emissions. This study investigates these aspects using a lab-scale fluidized bed reactor with flexible ammonia injection points. Key variables, such as ammonia co-firing ratios, injection location, temperature, and outlet oxygen concentration, are examined. The results show that with ammonia injection ratios up to 70 %, NO and N₂O emissions slightly increase, while ammonia escape is maintained below 5 ppm. Air staging effectively controls NO_x emissions, and higher temperatures promote N₂O decomposition, but increase NO_x levels. Ammonia injection does not raise unburned carbon content. Rate of production and sensitivity analyses highlight the role of OH radicals in ammonia conversion and identify the critical reactions affecting NO generation. This study highlights the feasibility of fluidized bed ammonia-coal co-firing technology.